1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus for obtaining image information by executing instruction sequence expressed by language for describing an image by means of a plurality of instruction processing devices.
2. Description of the Related Art
With the development of line printers suitable for high-speed digital printing such as electrophotography system and ink jet system, a printing control method using "page description language" has generally come into wide use which has broken from the conventional printing method, in which importance is attached to character information, and is capable of handling images, graphic forms, characters, etc. in the same manner, and freely controlling enlargement, rotation, and deformation of characters and graphic forms, etc. In the 1980's, various page description language were developed, and their representative examples are PostScript (trademark of Adobe Systems, Inc.) and Interpress (trademark of Xerox Inc.), and a large number of page description language are used for various printers.
In conventional page description language processing line printers, the central processing unit (CPU) in the line printer has interpreted successively, and the printer therein has carried out a printing operation. As an example thereof, it is described in Japanese Published Unexamined Patent Application No. Hei 1-188374 that there are provided a storage unit for receiving a program (hereinafter, referred to as printing information) for printing to be fed from a computer (hereinafter, referred to as host device) to store it, a processor for successively interpreting the printing information, and a line printer for printing in accordance with the printing information thus interpreted, so that, after the printing information is once transmitted from the host device to the line printer, the printing information is translated on the line printer side to carry out a printing operation to thereby reduce the load on the host device, thus improving the processing speed of the entire system.
In a decentralized environment using a network, however, a form in which a line printer is commonly used has become standard. The line printer should receive printing requests from a large number of host devices, and interpret and execute printing information described in page description language. If the line printer is used simultaneously by a large number of host devices, the waiting time until the result is obtained since printing is requested becomes long because the interpretation and execution of printing information described in the page description language in the line printer are performed in series. This situation has become more and more serious with the increased printing resolution.
Thus, in order to eliminate the aforesaid waiting time and form an image at high speed, a technique of interpreting and executing painting instructions in parallel has been proposed. In the technique disclosed in, for example, PCT/JP91/00456, formation and processing for a printed image are performed on a plurality of computers dispersed on a network, and the technique disclosed in Japanese Published Unexamined Patent Application No. Hei 7-104987 is to analyze and generate the image operating procedure in a document printing program for generating a parallel execution code.
In the aforesaid conventional parallel processing method, however, a division of instruction sequence is required to execute painting instructions in parallel, but the instruction sequence has not always been sufficiently divided. More specifically, in the technique disclosed in PCT/JP91/00456, the painting operation is executed in parallel as plural processes by dividing an area, on which an image is formed, in a band shape or in a mesh shape, but the parallelism of the painting instruction sequence actually inputted has not been sufficiently drawn out. Also, in the technique disclosed in Japanese Published Unexamined Patent Application No. Hei 7-104987, whether or not painting can be executed in parallel is determined by directly comparing the pixels, whereby the image has been formed so far, with pixels, whereby an image is formed by the execution of the next instruction, thus causing a great processing overhead. In this case, there is a possibility that a plenty of time will be consumed after all in consideration of total time from a time at which the user completes the editing operation and instructs printing to a time at which he obtains the page.
Further, in any of the aforesaid invention, as regards an area which cannot be divided because graphic forms are overlapped, processing should be successively performed, and this leads to a problem that the speed cannot be sufficiently increased.